How can I tell which 333 cpu's can also run at 266?

Aparently, according to a seller, his AthlonXP 2500+ barton (NIB Barton 2500+ PQZEA 0332) can also run at 266fsb (which is what my mb is).

How can I tell whcin of these bartons running over 266 can run at 266?

I think they all can but some of them will have locked multipliers so you'll want to find the unlocked ones. That's so you can raise the multipliers and get the stock or OCed speeds with a reduced fsb speed.

Any cpu that is 333 can run at 266. However, it will run slowly. If you take a 333 Barton that is supposed run with 2.166 ghz (13x166) and put it in a 266 motherboard, it will run at 266x13 = 1.729 ghz, so you lose a lot of speed.

In some cases, with older amd's (nothing that is currently manufactured, but stuff that was manufactured a year or more ago), you can unlock the multiplier, so you can raise the multiplier to compensate for the lower external frequency.

If you have a 266 motherboard, it probably does not have a bios available capable of recognizing a Barton, so you shouldn't buy a barton for it. Best case is it won't recognize the 512 cache and will run it like a 256. Worst case you won't even get the features of thoroughbred or palomino and it will just call it unrecognized cpu. In some cases, you can even lose SSE, it all depends on the bios and motherboard.

That being said, there is no advantage to using a 333 mhz chip, and it will require you physically modding the chip. To unlock mults you have to fill in the pits between the bridges with non conductive goop, then you have to use conductive paint or pencil to connect certain bridges. If you screw it up, you can be out a cpu.

All the new processors cannot be unlocked this way though.

heheh ahhh.. ok.... I think I'll just be buying a 266fsb cpu, i'm not into spending a week learning how to 'hack' a couple hundred MHz outa a cpu.